Rotary press with web-tensioning roll means

ABSTRACT

A rotary press of the offset or process engraving type comprises a plurality of printing units through which a paper web is fed in succession. Each unit comprises a power-driven blanket cylinder, a freely rotatable impression cylinder driven by frictional engagement with the paper web passing between the impression cylinder and the blanket cylinder and a tension control cylinder downstream of and driven from the impression cylinder at a peripheral speed slightly lower than that of the impression cylinder so that the tension T2 in the paper web between the impression cylinder and the tension control cylinder is slightly less than the tension T1 of the paper web entering the bite between the impression cylinder and the blanket cylinder. This tension differential avoids &#39;&#39;&#39;&#39;whipping&#39;&#39;&#39;&#39; or beating of the impression cylinder.

ire States Patent 1 3,633,504

[72] Inventor Louis Jean Chambon 864,166 6/1932 Barber lOl/228 Paris, France 996,639 4/1935 Brunnings 101/228 [21] Appl. No. 101,406 340,819 2/1944 Mills 101/228 X [22] Filed Dec. 24, 1970 426,680 2/1969 Kaufmann 101/228 X [45] Pa en J n-1 1972 1,653,199 12/1967 Belcher 101/228 X [73] Assignee Societe DEtudes Des Machines Speciales 2,151,961 3/1939 Erichsson. 101/182 Societe Anonyme 2,453,982 11/1948 Huck 101/181 Paris, France 2,723,620 11/1955 Huck 1 101/181 [32] Priority June 23, 1967 3,013,487 12/1961 Faeber 101/181 [33] France 3,179,045 4/1965 Evers lOl/18l [31] 111681 3,252,415 5/1966 Crawford 101/181 Continuation of application Ser. No. 738,061, June 18, 1968, now abandoned. j g jfg E l J L b t This application Dec. 24, 1970, Ser. No. nomeys 0 er urns an mmanue 0 a 0 101,406

ABSTRACT: A rotary press of the offset or process engraving ROTARY PRESS WITH WEB TENSIONING ROLL type comprises a plurality of printing units through which a MEANS pa er web 18 fed in succession. Each unit comprises a powerdriven blanket cylinder, a freely rotatable impression cylinder 4 Claims 2 Drawing Flgs' driven by frictional engagement with the paper web passing [52] U.S. Cl 101/228, between the impression cylinder and the blanket cylinder and 101/181, 101/219 a tension control cylinder downstream of and driven from the [51] Int. Cl 1341f 5/06 impression cylinder at a peripheral speed slightly lower than [50] Field of Search 101/181, that of the impression cylinder so that the tension T in the 225, 228, 219, 178 paper web between the impression cylinder and the tension control cylinder is slightly less than the tension T of the paper [56] References Cited web entering the bite between the impression cylinder and the UNITED STATES PATENTS blanket cylinder. This tension differential avoids whipping" 870,210 1 1/1967 Wood 101 225 or beating of the impression Cylinder 938,381 lO/l909 Huffman lOl/228 ROTARY PRESS WITH WEB-TENSIONING ROLL MEANS This application is a continuation of Ser. No. 738,061, filed June 18, I968, now abandoned.

BACKGROUND OF THE INVENTION The present invention relates in general to improvements in or relating to rotary presses and has specific reference to machines of the offset or process engraving type.

In printing machines of the above-mentioned type a variation in the tension of the paper web as a function of the velocity of rotation of the rotary press is observed, this variation being related to the specific nature of the web material. As a rule, this tension is moderate at low machine speeds and increases with the rotational velocity.

Therefore, in a rotary press adapted to print several colors in one run it may happen that the tension of the paper web varies by decreasing from one printing device to another, at low machine speed, and that on the other hand this tension increases from one device to another at higher rotational speeds of the press. Under these conditions a tension gradient which is negative at low speeds and positive at high speeds is observed. Due to the mechanical play intervening in the drive associated with the various printing devices, it is clear that a relative shift can take place between the printing cylinders when the (positive or negative) sign of the tension gradient is reversed, this shift being highly detrimental to the precision in the printing of the various colors.

SUMMARY OF THE INVENTION It is the essential object of the present invention to avoid this inconvenience by resorting to a device of particularly simple design and construction.

To this end, the rotary press of the offset or process engraving type, which comprises a plurality of printing devices through which a paper web is fed in succession, each printing device comprising a blanket cylinder or an engraved cylinder and an impression cylinder, between which the paper web is fed continuously, is characterized in that the paper web is caused, downstream of each pair of cylinders of a printing device, to pass over a tension-control cylinder rotatably driven at a tangential speed which is constantly proportional to, and slightly lower than, the linear speed of said upper paper web, whereby said web is caused to slip in relation to the surface of said tension-control cylinder and therefore retarded.

This invention is advantageous in that the frictional contact thus created between the said tension-control cylinder and said paper web causes the web tension downstream of the pair of impression cylinders to be constantly lower than the upstream tension, irrespective of the velocity of rotation of the rotary press. Thus, any lack of precision in the printing process is definitely avoided since the difference between the web tension upstream of a pair of impression cylinders and the web tension downstream of these cylinders has always the same algebraic sign, irrespective of other operating conditions. Therefore, the mechanical play existing in the transmission system is constantly taken up in the same direction.

BRIEF DESCRIPTION OF THE DRAWING Various forms of embodiment of this invention will now be described by way of example with reference to the accompanying drawing in which:

FIG. 1 is a diagram showing a printing device incorporated in an offset rotary press;

FIG. 2 is another diagram showing the printing device of a process-engraving machine.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring first to FIG. 1, showing only one printing device of an offset rotary press comprising, in a manner well known to those conversant with the art, as many printing devices as there are colors in the final print, page or sheet, this printing device comprises essentially a hard engraved or plate cylinder l revolving about a shaft 2 and tangent to a blanket cylinder 3 lined with a peripheral rubber layer and revolving about another shaft 4. The drive between shafts 2 and 4 is through gears comprising pinions 5, 6, 7 and 8.

The paper web on which the printing is to be performed runs between the blanket cylinder 3 and a lower impression cylinder 11 having its shaft 12 mounted for free rotation on the frame structure of the machine. In other words, the lower impression cylinder 11 is rotatably driven only as a consequence of the frictional engagement obtaining between its outer peripheral surface and the paper web 9 pressed between the blanket cylinder 3 and this lower impression cylinder 11.

Downstream of the pair of cylinders 3 and 11 and beneath paper web 9 is a tension-control cylinder 13 having its shaft 14 rotatably mounted on the frame structure of the device. This cylinder 13 is disposed at a level slightly above that of the impression cylinder 11 whereby the paper web 9 pressed between the cylinders 3 and 11 along the lower contact generatrix A of cylinder 3 is kept, downstream of this generatrix A, in close engagement with the outer surface of the blanket cylinder 3 along an arc AB of about 30. At this point B the web 9 leaves the surface of blanket cylinder 3 and engages the surface of the aforesaid tension-control cylinder 13 at a point C, and remains in contact therewith up to another point D corresponding to a horizontal tangent whereat the web leaves the cylinder 13.

This tension-control cylinder 13 is rotatably driven in a positive manner from the impression cylinder 11 by means of a train of gears comprising a pinion l5 rigid with shaft 12, an intermediate pinion l6 and a final pinion l7 rigid with shaft 14. The transmission ratio of this train of gears is selected to cause the tangential speed of tension-control cylinder 13 to be slightly lower than the web speed, that is, than the tangential speed of impression cylinder 11, while being constantly proportional to this last-named speed. Thus, for instance, the tangential speed of cylinder 13 may be 5 percent lower than the linear speed of paper web 9.

Under these conditions, since the web speed is constantly slightly greater than the tangential speed of the tension-control cylinder 13, this web 9 is slightly retarded as it passes over this cylinder and as a result the web tension T downstream of cylinders 3 and 11 is constantly kept at a value slightly lower than the tension T measured upstream of these cylinders, irrespective of the velocity of rotation of the press.

As the difference T,T is constantly positive, the mechanical play existing or developing in the motion control system is constantly taken up in the same direction and a very high degree of precision in the printing process is obtained.

In the case of a process engraving press illustrated diagrammatically in FIG. 2 the paper web 9, after having passed over different guide cylinders l8, l9 and 21 is inserted between the lower engraved or plate cylinder 22 dipping in the ink-trough 23 and an upper impression cylinder 24. The web 9 then passes over a tension-control cylinder 25 and another set of guide cylinders 26, 27 and 28.

As in the case illustrated in FIG. I, the tension-control cylinder 25 is rotatably and positively driven from the upper impression cylinder 24 by means of a train of gears designated as a whole by the reference numeral 29. In this case too the transmission ratio provided by the train of gears 29 is calculated to cause the tangential speed of the tension-control cylinder 25 to be constantly slightly lower and proportional to the linear speed of the paper web 9, whereby the web tension downstream of the printing devices is constantly lower than the web tension measured upstream thereof.

Of course, the forms of embodiment of the invention which have been described hereinabove with reference to the attached drawings should not be construed as limiting the field of the invention since many modifications may be brought thereto without departing from the spirit and scope of the invention.

What I claim and desired to secure by Letters Patent is:

l. A rotary press of the offset or process engraving type comprising a plurality of printing units through which a paper web is fed in direct succession, each of said units comprising a power-driven blanket cylinder and a cooperating impression cylinder mounted for free rotation and driven by frictional engagement with the paper web passing in the nip between the blanket cylinder and the impression cylinder with an entering tension T a tension control cylinder to which the paper web is directed directly downstream of said blanket cylinder and impression cylinder said web contacting said tension control cylinder only on the downstream side of said nip and means for driving said tension control cylinder from said impression cylinder at a circumferential speed which is constantly proportional to and slightly lower than that of said impression cylinder so that the tension T of the paper web between said tension control cylinder and said blanket cylinder is slightly lower than said tension T thereby avoiding beating of said impression cylinder.

2. A rotary press according to claim I, in which said impression cylinder is below said blanket cylinder and said tension control cylinder is offset upwardly relative to said impression cylinder.

3. A rotary press according to claim 1, in which said paper web engages said tension control cylinder for an arc of less than 4. A rotary press according to claim 1, in which said means for driving said tension control cylinder comprises a gear train between said impression cylinder and said tension control cylinder. 

1. A rotary press of the offset or process engraving type comprising a plurality of printing units through which a paper web is fed in direct succession, each of said units comprising a power-driven blanket cylinder and a cooperating impression cylinder mounted for free rotation and driven by frictional engagement with the paper web passing in the nip between the blanket cylinder and the impression cylinder with an entering tension T1, a tension control cylinder to which the paper web is directed directly downstream of said blanket cylinder and impression cylinder said web contacting said tension control cylinder only on the downstream side of said nip and means for driving said tension control cylinder from said impression cylinder at a circumferential speed which is constantly proportional to and slightly lower than that of said impression cylinder so that the tension T2 of the paper web between said tension control cylinder and said blanket cylinder is slightly lower than said tension T1, thereby avoiding beating of said impression cylinder.
 2. A rotary press according to claim 1, in which said impression cylinder is below said blanket cylinder and said tension control cylinder is offset upwardly relative to said impression cylinder.
 3. A rotary press according to claim 1, in which said paper web engages said tension control cylinder for an arc of less than 90*.
 4. A rotary press according to claim 1, in which said means for driving said tension control cylinder comprises a gear train between said impression cylinder and said tension control cylinder. 